Refactoring

# Before
def process_order(order):
    if not order.items:
        raise ValueError("Empty order")
    if order.total < 0:
        raise ValueError("Negative total")
    tax = order.total * 0.18
    return order.total + tax

# After
def _validate_order(order):
    if not order.items:
        raise ValueError("Empty order")
    if order.total < 0:
        raise ValueError("Negative total")

def _compute_total_with_tax(order):
    TAX_RATE = 0.18
    return order.total + order.total * TAX_RATE

def process_order(order):
    _validate_order(order)
    return _compute_total_with_tax(order)

# Before
def calculate_tax(amount):
    return amount * 0.18

# After
TAX_RATE = 0.18

def calculate_tax(amount):
    return amount * TAX_RATE

# Before
def calculate_total(items):
    return sum(item.price for item in items)

# After
def calculate_total(items):
    """Calculate total price for list of items.

    Args:
        items: List of items with price attribute

    Returns:
        Total sum of item prices
    """
    return sum(item.price for item in items)

# Before
if not (x < 10 or x > 20):
    process()

# After
if 10 <= x <= 20:
    process()

# Before
def create_user(name, email, age, city, country):
    pass

# After
from dataclasses import dataclass

@dataclass
class UserData:
    name: str
    email: str
    age: int
    city: str
    country: str

def create_user(user: UserData):
    pass